Full cell stack

ABSTRACT

A fuel cell stack is provided with an outlet side oxygen-containing gas communication hole. First and second oxygen-containing gas flow passage grooves are provided in the direction of the gravity while meandering in the horizontal direction on a surface of a first separator. The second oxygen-containing gas flow passage grooves communicate with the outlet side oxygen-containing gas communication hole via second oxygen-containing gas connecting flow passages. A porous water-absorbing tube, which is used to discharge water to the outside of the fuel cell stack in accordance with the capillary phenomenon and the difference in pressure of air, is provided for the outlet side oxygen-containing gas communication hole.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell stack which comprises afuel cell unit composed of a solid polymer ion exchange membraneinterposed between an anode electrode and a cathode electrode, andseparators for supporting the fuel cell unit interposed therebetween,the fuel cell units and the separators being stacked in the horizontaldirection. The fuel cell stack is especially appropriate to be carriedon a vehicle.

2. Description of the Related Art

For example, the solid polymer type fuel cell comprises a fuel cell unitincluding an anode electrode and a cathode electrode disposed opposinglyon both sides of an electrolyte composed of a polymer ion exchangemembrane (cation exchange membrane) respectively, the fuel cell unitbeing interposed between separators. Usually, the solid polymer typefuel cell is used as a fuel cell stack obtained by stacking apredetermined number of the fuel cell units.

In such a fuel cell stack, a fuel gas, i.e., a gas principallycontaining hydrogen (hereinafter referred to as “hydrogen-containinggas”) which is supplied to the anode electrode, hydrogen being convertedinto ion on the catalyst electrode, is moved toward the cathodeelectrode via the electrolyte which is appropriately humidified. Theelectron, which is generated during this process, is extracted for anexternal circuit, and the electron is utilized as DC electric energy. Anoxygen-containing gas such as a gas principally containing oxygen(hereinafter referred to as “oxygen-containing gas”) or air is suppliedto the cathode electrode. Therefore, the hydrogen ion, the electron, andthe oxygen are reacted with each other on the cathode electrode, andthus water is produced.

In the fuel cell stack described above, an internal manifold isconstructed in order to supply the fuel gas and the oxygen-containinggas (reaction gas) to the anode electrode and the cathode electrode ofeach of the stacked fuel cell units respectively. Specifically, theinternal manifold includes a plurality of communication holes which areprovided in an integrated manner to make communication with each of thefuel cell units and the separators which are stacked with each other.When the reaction gas is supplied to the supplying communication hole,the reaction gas is supplied in a dispersed manner to each of the fuelcell units, while the used reaction gas is integrally discharged to thedischarging communication hole.

The reaction product water, which is generated on the electrodepower-generating surface, tends to be introduced especially into thecommunication hole through which the oxygen-containing gas flows.Retained water exists in the communication hole in many cases. On theother hand, it is feared that any retained water is generated due tocondensation of water vapor or the like in the communication holethrough which the fuel gas flows. Therefore, the following inconvenienceis pointed out. That is, the communication hole is reduced in crosssectional area or closed by the retained water, and the smooth flow ofthe reaction gas is prevented. As a result, the power generationperformance is deteriorated.

In view of the above, for example, as disclosed in Japanese Laid-OpenPatent Publication No. 8-138692, a fuel cell is known, in whichhydrophilic coating films are provided for a fuel gas flow passage andan oxygen-containing gas flow passage formed on a stacking surface of acollector electrode. Specifically, as shown in FIG. 26, supply/dischargeflow passages 2 a, 2 b for the fuel gas are formed to penetrate throughboth side portions of a collector electrode 1. Supply/discharge flowpassages 3 a, 3 b are formed to penetrated through upper and lowerportions of the collector electrode 1. A plurality of oxygen-containinggas flow passages 4, which are parallel to one another in the verticaldirection, are provided linearly on the side of the power-generatingsurface of the collector electrode 1. A hydrophilic coating film 5 isformed for the oxygen-containing gas flow passage 4. A porous member 6is arranged for the oxygen-containing gas supply/discharge flow passage3 b.

In the arrangement as described above, when the water, which is producedon the side of the power-generating surface in accordance with theoperation of the fuel cell, is introduced into the oxygen-containing gasflow passages 4, the product water humidifies the hydrophilic coatingfilm 5 formed for the oxygen-containing gas flow passage 4. The productwater flows vertically downwardly along the hydrophilic coating film 5and its surface, and it is discharged from the oxygen-containing gasflow passage 4. Further, the product water is absorbed by the porousmember 6 which is arranged for the oxygen-containing gassupply/discharge flow passage 3 b. As a result, it is stated that theproduct water can be reliably discharged from the oxygen-containing gasflow passage 4.

However, in the case of the conventional technique described above, theoxygen-containing gas supply/discharge flow passages 3 a, 3 b are formedat the upper and lower portions of the collector electrode 1. Therefore,it is difficult to shorten the size of the entire fuel cell in theheight direction. Especially, in the case of the use as a fuel cellstack to be carried on a vehicle, it is necessary to effectively utilizethe space, e.g., under the floor of the automobile body. It is demandedto shorten the size of the entire fuel cell in the height direction assmall as possible. However, the conventional technique described aboveinvolves such a problem that it is impossible to effectively respond tothe demand.

Further, the oxygen-containing gas supply/discharge flow passages 3 a, 3b are formed to be lengthy in the lateral direction at the upper andlower portions of the collector electrode 1. For this reason, in orderto ensure the rigidity of the collector electrode 1, it is necessary toset a relatively large thickness of the collector electrode 1.Accordingly, the problem is pointed out that the size of the entire fuelcell stack in the stacking direction is lengthy.

When the size of the entire fuel cell stack in the stacking direction islengthy, the oxygen-containing gas supply/discharge flow passage 3 bbecomes long in the stacking direction. The problem also arises that theproduct water or the like existing at the deep side is difficult to bedischarged. Especially, when the fuel cell stack is used to be carriedon the vehicle, it is feared that the vehicle runs in an inclined state,and the product water is retained at the deep portion of theoxygen-containing gas supply/discharge flow passage 3 b. At that time,the problem arises that the power generation performance is deterioratedbecause the product water is not discharged.

A technique is disclosed in Japanese Laid-Open Patent Publication No.10-284096, in which water droplets are prevented from invasion into thepower-generating surface by providing a gas branch groove which extendsdownwardly from a gas inlet of a communication hole. However, when thegas branch groove is provided for the power-generating surface, theamount of gas, which is discharged without contributing to the powergeneration, is increased. Then, the problem arises such that the ratioof utilization of the reaction gas is lowered, resulting in the decreasein efficiency of the entire system.

A technique is disclosed in U.S. Pat. No. 4,968,566, in which waterdischarge ports are provided at lower four corner portions of a fuelcell, and the discharge ports are switched depending on a signal of aninclination sensor. However, the problem arises that the structure ofthe apparatus is considerably complicated.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a fuel cellstack which has a function to smoothly and reliably discharge water.

A principal object of the present invention is to provide a fuel cellstack which has a function to smoothly and reliably discharge water andwhich makes it possible to shorten the size in the height direction assmall as possible and effectively realize a thin-walled thickness of aseparator.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which a preferredembodiment of the present invention is shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic longitudinal sectional view illustrating a fuelcell stack according to a first embodiment of the present invention;

FIG. 2 shows an exploded perspective view illustrating major componentsof the fuel cell stack shown in FIG. 1;

FIG. 3 shows a schematic sectional view illustrating the fuel cell stackshown in FIG. 1;

FIG. 4 shows a front view illustrating a first separator whichconstitutes the fuel cell stack shown in FIG. 1;

FIG. 5 shows a front view illustrating a first surface of a secondseparator which constitutes the fuel cell stack shown in FIG. 1;

FIG. 6 shows a front view illustrating a second surface of the secondseparator;

FIG. 7 shows a perspective view illustrating a porous water-absorbingtube and the first separator which constitute the fuel cell stack shownin FIG. 1;

FIG. 8 shows a perspective view with partial cross section illustratingwire members which constitute the porous water-absorbing tube;

FIG. 9 illustrates a static pressure distribution in the fuel cell stackshown in FIG. 1;

FIG. 10 shows a perspective view illustrating a porous water-absorbingtube and a first separator which constitute a fuel cell stack accordingto a second embodiment of the present invention;

FIG. 11 shows a partial perspective view illustrating a porouswater-absorbing tube which constitutes a fuel cell stack according to athird embodiment of the present invention;

FIG. 12 shows a partial perspective view illustrating a porouswater-absorbing tube which constitutes a fuel cell stack according to afourth embodiment of the present invention;

FIG. 13 shows a longitudinal sectional view illustrating a fuel cellstack according to a fifth embodiment of the present invention;

FIG. 14 shows a vertical sectional view illustrating a porouswater-absorbing tube which constitutes a fuel cell stack according to asixth embodiment of the present invention;

FIG. 15 shows a schematic longitudinal sectional view illustrating afuel cell stack according to a seventh embodiment of the presentinvention;

FIG. 16 shows an exploded perspective view illustrating major componentsof the fuel cell stack;

FIG. 17 shows a front view illustrating a first surface of a bypassplate;

FIG. 18 shows a sectional view of the bypass plate taken along a lineB-B shown in FIG. 17 and an exploded side view of other members;

FIG. 19 shows a schematic view diagrammatically illustrating a fuel cellstack according to a seventh embodiment of the present invention;

FIG. 20 shows a schematic view illustrating a layout of a bypass flowpassage according to an eighth embodiment of the present invention;

FIG. 21 shows a schematic view illustrating a layout of a bypass flowpassage according to a ninth embodiment of the present invention;

FIG. 22 shows a schematic vertical sectional view illustrating a fuelcell stack according to a tenth embodiment of the present invention;

FIG. 23 shows a sectional view illustrating an attached state of amanifold tube and a drainage pipe;

FIG. 24 shows a sectional view illustrating an inserted situation of thedrainage pipe;

FIG. 25 shows a front view illustrating the drainage pipe shown in FIG.24; and

FIG. 26 shows a perspective view illustrating a collector electrodeconcerning the conventional technique.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic longitudinal sectional view illustrating a fuelcell stack 10 according to a first embodiment of the present invention,and FIG. 2 shows an exploded perspective view illustrating majorcomponents of the fuel cell stack 10 described above.

The fuel cell stack 10 comprises a fuel cell unit 12, and first andsecond separators 14, 16 for supporting the fuel cell unit 12 interposedtherebetween. A plurality of sets of these components are stacked witheach other. The fuel cell unit 12 includes a solid polymer ion exchangemembrane 18, and a cathode electrode 20 and an anode electrode 22 whichare arranged with the ion exchange membrane 18 intervening therebetween.First and second gas diffusion layers 24, 26, each of which is composedof, for example, porous carbon paper as a porous layer, are arranged forthe cathode electrode 20 and the anode electrode 22.

First and second gaskets 28, 30 are provided on both sides of the fuelcell unit 12. The first gasket 28 has a large opening 32 foraccommodating the cathode electrode 20 and the first gas diffusion layer24. On the other hand, the second gasket 30 has a large opening 34 foraccommodating the anode electrode 22 and the second gas diffusion layer26. The fuel cell unit 12 and the first and second gaskets 28, 30 areinterposed between the first and second separators 14, 16. A thirdgasket 35 is arranged for the second separator 16.

The first separator 14 is provided, at its upper portions at the bothends in the lateral direction, with an inlet side fuel gas communicationhole 36 a for allowing a fuel gas (reaction gas) such as hydrogen gas topass therethrough, and an inlet side oxygen-containing gas communicationhole 38 a for allowing an oxygen-containing gas (reaction gas) as a gascontaining oxygen or air to pass therethrough.

The first separator 14 is provided, at its central portions at the bothends in the lateral direction, with an inlet side cooling mediumcommunication hole 40 a for allowing a cooling medium such as purewater, ethylene glycol, and oil to pass therethrough, and an outlet sidecooling medium communication hole 40 b for allowing the cooling mediumafter being used to pass therethrough. The first separator 14 isprovided, at its lower portions at the both ends in the lateraldirection, with an outlet side fuel gas communication hole 36 b forallowing the fuel gas to pass therethrough, and an outlet sideoxygen-containing gas communication hole 38 b for allowing theoxygen-containing gas to pass therethrough so that the outlet side fuelgas communication hole 36 b and the outlet side oxygen-containing gascommunication hole 38 b are disposed at diagonal positions with respectto the inlet side fuel gas communication hole 36 a and the inlet sideoxygen-containing gas communication hole 38 a respectively.

A plurality of, for example, six of mutually independent firstoxygen-containing gas flow passage grooves (gas flow passages) 42, areprovided closely to the inlet side oxygen-containing gas communicationhole 38 a so that they are directed in the direction of the gravitywhile meandering in the horizontal direction on the surface 14 a opposedto the cathode electrode 20 of the first separator 14. The firstoxygen-containing gas flow passage grooves 42 are merged into threesecond oxygen-containing gas flow passage grooves (gas flow passages)44. The second oxygen-containing gas flow passage grooves 44 terminateat positions close to the outlet side oxygen-containing gascommunication hole 38 b.

As shown in FIGS. 2 to 4, the first separator 14 is provided with firstoxygen-containing gas connecting flow passages 46 which penetratethrough the first separator 14, which communicate at first ends with theinlet side oxygen-containing gas communication hole 38 a on the surface14 b on the side opposite to the surface 14 a, and which communicate atsecond ends with the first oxygen-containing gas flow passage grooves 42on the side of the surface 14 a, and second oxygen-containing gasconnecting flow passages 48 which communicate at first ends with theoutlet side oxygen-containing gas communication hole 38 b on the side ofthe surface 14 b and which communicate at second ends with the secondoxygen-containing gas flow passage grooves 44 on the side of the surface14 a to penetrate through the first separator 14.

As shown in FIG. 2, an inlet side fuel gas communication hole 36 a, aninlet side oxygen-containing gas communication hole 38 a, an inlet sidecooling medium communication hole 40 a, an outlet side cooling mediumcommunication hole 40 b, an outlet side fuel gas communication hole 36b, and an outlet side oxygen-containing gas communication hole 38 b areformed at both end portions in the lateral direction of the secondseparator 16, in the same manner as in the first separator 14.

As shown in FIG. 5, a plurality of, for example, six of first fuel gasflow passage grooves (gas flow passages) 60 are formed closely to theinlet side fuel gas communication hole 36 a on the surface 16 a of thesecond separator 16. The first fuel gas flow passage grooves 60 extendin the direction of the gravity while meandering in the horizontaldirection, and they are merged into three second fuel gas flow passagegrooves (gas flow passages) 62. The second fuel gas flow passage grooves62 terminate in the vicinity of the outlet side fuel gas communicationhole 36 b.

The second separator 16 is provided with first fuel gas connecting flowpassages 64 for communicating the inlet side fuel gas communication hole36 a with the first fuel gas flow passage grooves 60 from the side ofthe surface 16 b,and second fuel gas connecting flow passages 66 forcommunicating the outlet side fuel gas communication hole 36 b with thesecond fuel gas flow passage grooves 62 from the side of the surface 16b to penetrate through the second separator 16.

As shown in FIGS. 3 and 6, a stepped section 70, which corresponds to anopening 68 of the third gasket 35, is formed on the surface 16 b of thesecond separator 16. A plurality of main flow passage grooves 72 a, 72 bfor constructing cooling medium flow passages are formed in the steppedsection 70 closely to the inlet side cooling medium communication hole40 a and the outlet side cooling medium communication hole 40 b.Branched flow passage grooves 74, which are branched into a plurality ofindividuals respectively, are provided to extend in the horizontaldirection between the main flow passage grooves 72 a, 72 b.

The second separator 16 is provided with first cooling medium connectingflow passages 76 for making communication between the inlet side coolingmedium communication hole 40 a and the main flow passage grooves 72 a,and second cooling medium connecting flow passages 78 for makingcommunication between the outlet side cooling medium communication hole40 b and the main flow passage grooves 72 b to penetrate through thesecond separator 16.

As shown in FIG. 2, an inlet side fuel gas communication hole 36 a, aninlet side oxygen-containing gas communication hole 38 a, an inlet sidecooling medium communication hole 40 a, an outlet side cooling mediumcommunication hole 40 b, an outlet side fuel gas communication hole 36b, and an outlet side oxygen-containing gas communication hole 38 b areprovided at both end portions in the lateral direction of each of thefirst, second, and third gaskets 28, 30, 35.

As shown in FIG. 1, first and second end plates 80, 82 are arranged atboth ends in the stacking direction of the fuel cell units 12 and thefirst and second separators 14, 16. The first and second end plates 80,82 are integrally tightened and fastened by the aid of tie rods 84.

A porous water-absorbing tube 86 is arranged to extend in the stackingdirection for at least the outlet side oxygen-containing gascommunication holes 38 b and optionally for the outlet side fuel gascommunication holes 36 b in the fuel cell stack 10. As shown in FIGS. 1and 7, the porous water-absorbing tube 86 includes a pipe-shaped coremember 88 which is made of metal, for example, SUS (stainless steel),and a plurality of wire members 90 which are wound around the outercircumference of the core member 88.

As shown in FIG. 8, the wire member 90 has irregularities on thesurface. The respective wire members 90 are bundled, and thus a space 92is formed. The space 92 extends in the longitudinal direction of thecore member 88 (in the stacking direction of the fuel cell stack 10).Both ends of the core member 88 may be closed. The core member 88 isfixed in the fuel cell stack 10 by the aid of an unillustrated fixingmeans.

As shown in FIGS. 4 and 5, the porous water-absorbing tubes 86 areinstalled on the lower side in the direction of the gravity at thepositions separated from the second oxygen-containing gas connectingflow passages 48 and the second fuel gas connecting flow passages 66, inthe outlet side oxygen-containing gas communication holes 38 b and theoutlet side fuel gas communication holes 36 b.

As shown in FIG. 1, the first end plate 80 is formed with a hole 94which communicates with the outlet side oxygen-containing gascommunication hole 38 b. A manifold tube 98, which communicates with thehole 94, is connected to the first end plate 80 via a joint 96. Themanifold tube 98 is provided with an outer tube 100 which is bentupwardly from the joint 96. A porous water-absorbing tube 102, which isconnected to the porous water-absorbing tube 86 or which is elongatedfrom the porous water-absorbing tube 86, is arranged in the outer tube100. The porous water-absorbing tube 102 is connected, for example, to awater storage tank (not shown) for storing water which is usable tohumidify and reform the gas.

The first end plate 80 is formed with a hole 104 which communicates withthe outlet side fuel gas communication hole 36 b. A manifold tube 106,which is constructed in the same manner as the manifold tube 98described above, is connected to the hole 104, detailed explanation ofwhich is omitted.

The operation of the fuel cell stack 10 according to the firstembodiment constructed as described above will be explained below.

The fuel gas, for example, the gas containing hydrogen obtained byreforming hydrocarbon is supplied to the inside of the fuel cell stack10, and the air or the gas containing oxygen as the oxygen-containinggas (hereinafter simply referred to as “air”) is supplied thereto.Further, the cooling medium is supplied in order to cool thepower-generating surface of the fuel cell unit 12. As shown in FIGS. 3and 5, the fuel gas, which is supplied to the inlet side fuel gascommunication hole 36 a in the fuel cell stack 10, is moved from theside of the surface 16 b to the side of the surface 16 a via the firstfuel gas connecting flow passages 64. The fuel gas is supplied to thefirst fuel gas flow passage grooves 60 which are formed on the side ofthe surface 16 a.

The fuel gas, which is supplied to the first fuel gas flow passagegrooves 60, is moved in the direction of the gravity while meandering inthe horizontal direction along the surface 16 a of the second separator16. During this process, the hydrogen-containing gas in the fuel gaspasses through the second gas diffusion layer 26, and it is supplied tothe anode electrode 22 of the fuel cell unit 12. The unreacted fuel gasis supplied to the anode electrode 22 while being moved along the firstfuel gas flow passage grooves 60. On the other hand, the fuel gas, whichis not used, passes through the second fuel gas flow passage grooves 62,and it is introduced into the second fuel gas connecting flow passages66. The fuel gas is moved toward the side of the surface 16 b, and thenit is discharged to the outlet side fuel gas communication hole 36 b.

As shown in FIG. 3, the air, which is supplied to the inlet sideoxygen-containing gas communication hole 38 a in the fuel cell stack 10,is introduced into the first oxygen-containing gas flow passage grooves42 via the first oxygen-containing gas connecting flow passages 46 whichcommunicate with the inlet side oxygen-containing gas communication hole38 a of the first separator 14. As shown in FIG. 2, the air, which issupplied to the first oxygen-containing gas flow passage grooves 42, ismoved in the direction of the gravity while meandering in the horizontaldirection. During this process, the oxygen-containing gas in the air issupplied from the first gas diffusion layer 24 to the cathode electrode20. On the other hand, the air, which is not used, passes through thesecond oxygen-containing gas flow passage grooves 44, and it isdischarged from the second oxygen-containing gas connecting flowpassages 48 to the outlet side oxygen-containing gas communication hole38 b. Accordingly, the electric power is generated in the fuel cell unit12. For example, the electric power is supplied to an unillustratedmotor.

Further, the cooling medium, which is supplied to the inside of the fuelcell stack 10, is introduced into the inlet side cooling mediumcommunication hole 40 a, and then it is supplied to the main flowpassage grooves 72 a on the side of the surface 16 b via the firstcooling medium connecting flow passages 76 of the second separator 16 asshown in FIG. 6. The cooling medium passes through the plurality ofbranched flow passage grooves 74 which are branched from the main flowpassage grooves 72 a to cool the power-generating surface of the fuelcell unit 12, followed by being merged into the main flow passagegrooves 72 b. The cooling medium after the use passes through the secondcooling medium connecting flow passages 78, and it is discharged fromthe outlet side cooling medium communication hole 40 b.

During the period in which the fuel cell stack 10 is operated asdescribed above, a relatively large amount of water is producedespecially on the side of the cathode electrode 20. The water isdischarged to the outlet side oxygen-containing gas communication hole38 b via the first and second oxygen-containing gas flow passage grooves42, 44.

In this case, in the first embodiment, the porous water-absorbing tube86 is arranged for the outlet side oxygen-containing gas communicationhole 38 b. The water, which is introduced into the outlet sideoxygen-containing gas communication hole 38 b, is transmitted inaccordance with the capillary phenomenon through the plurality of wiremembers 90 which constitute the porous water-absorbing tube 86. Thewater is introduced into the space 92 formed among the wire members 90.In the fuel cell stack 10, the oxygen-containing gas and the fuel gashave the static pressure distribution as shown in FIG. 9. Accordingly,the pressure on the outlet side of the outlet side oxygen-containing gascommunication hole 38 b is lower than the pressure on the inner side.The water, which is introduced into the space 92 of the porouswater-absorbing tube 86, is extruded by the difference in pressurebetween upper and lower streams of air toward the first end plate 80,i.e., toward the manifold tube 98 as shown by the direction of the arrowA in FIG. 1.

Accordingly, in the first embodiment, the water, which is introducedinto the outlet side oxygen-containing gas communication hole 38 b, isdischarged smoothly and reliably toward the porous water-absorbing tube102 in the manifold tube 98 owing to the capillary phenomenon of theporous water-absorbing tube 86 and the difference in pressure of air inthe outlet side oxygen-containing gas communication hole 38 b. Accordingto the simple structure, an effect is obtained that the drainageperformance for the retained condensed water such as the product wateris effectively improved.

Especially, when the fuel cell stack 10 is carried on the vehicle, evenif the fuel cell stack 10 is inclined, for example, due to anyinclination of the running road, then the water, which is introducedinto the outlet side oxygen-containing gas communication hole 38 b,makes no back flow toward the second oxygen-containing gas flow passagegroove 44. Therefore, the following advantage is obtained. That is, itis possible to prevent the electrode power-generating surface from beingcovered with the product water in the fuel cell stack 10, and it is alsopossible to reliably avoid the deterioration of the power generationperformance.

Further, as shown in FIG. 4, the porous water-absorbing tube 86 isarranged on the lower side in the direction of the gravity of the outletside oxygen-containing gas communication hole 38 b at the positionseparated from the second oxygen-containing gas connecting flow passages48. Accordingly, the water-absorbing performance for the product wateris improved. It is also possible to avoid the disturbance of the flowdistribution of the air on the side of the electrode power-generatingsurface of the first separator. Further, the pressure loss of the air isnot increased in the outlet side oxygen-containing gas communicationhole 38 b.

As shown in FIG. 1, the manifold tube 98 is bent upwardly. The porouswater-absorbing tube 102, which is arranged in the manifold tube 98, isarranged at the position higher than the outlet side oxygen-containinggas communication hole 38 b. Accordingly, it is possible to make thelayout of the manifold tube 98 in the plane of the first end plate 80.The size of the entire fuel cell stack 10 in the height direction is notincreased. Therefore, the following advantage is obtained. That is, thedegree of freedom of the piping layout is improved. It is possible toeffectively shorten the size in the height direction of the entire fuelcell stack 10. The fuel cell stack 10 is especially excellent when it iscarried on the vehicle.

In the first embodiment, as shown in FIG. 2, the inlet side fuel gascommunication hole 36 a, the inlet side oxygen-containing gascommunication hole 38 a, the inlet side cooling medium communicationhole 40 a, the outlet side cooling medium communication hole 40 b, theoutlet side fuel gas communication hole 36 b, and the outlet sideoxygen-containing gas communication hole 38 b are provided at the bothend portions in the lateral direction of the fuel cell stack 10.Accordingly, it is unnecessary to provide any lengthy communication holein the lateral direction, at upper and lower portions of the fuel cellstack 10. The size in the height direction of the entire fuel cell stack10 can be as short as possible, and the strength is also improved.Therefore, it is possible to effectively make thinner the size of theentire fuel cell stack 10 in the stacking direction.

In the first embodiment, explanation has been made for those disposed onthe side of the outlet side oxygen-containing gas communication hole 38b. The condensed water is similarly produced on the side of the outletside fuel gas communication hole 36 b as well. It is possible to providethe efficient and reliable drainage function by using the porouswater-absorbing tube 86. Although the porous water-absorbing tube 86 hasthe pipe-shaped core member 88, it is also preferable to use arod-shaped member alternatively.

In the first embodiment, the first and second oxygen-containing gas flowpassage grooves 42, 44, which are the gas flow passage grooves, areprovided in the direction of the gravity while meandering in thehorizontal direction on the surface 14 a of the first separator 14. Onthe other hand, the first and second fuel gas flow passage grooves 60,62, which are the gas flow passages, are provided in the direction ofthe gravity while meandering in the horizontal direction on the surface16 a of the second separator 16. Alternatively, the respective gas flowpassages may be provided in the direction of the antigravity whilemeandering in the horizontal direction on the surfaces 14 a, 16 a of thefirst and second separators 14, 16. In this arrangement, the porouswater-absorbing tubes 86 are arranged on the upper side of the first andsecond separators 14, 16. However, the same effect is obtained, forexample, that the drainage performance for the retained condensed wateris effectively improved owing to the capillary phenomenon of the porouswater-absorbing tube 86 and the difference in pressure of air or thelike.

FIG. 10 shows a perspective view illustrating a porous water-absorbingtube 120 and a first separator 14 which constitute a fuel cell stackaccording to a second embodiment of the present invention. The sameconstitutive components as those of the fuel cell stack 10 according tothe first embodiment are designated by the same reference numerals,detailed explanation of which will be omitted. Explanation will be madein the second embodiment and the following described below in the samemanner as described above.

The porous water-absorbing tube 120 comprises a pipe member 122 made ofmetal, for example, SUS, and a plurality of wire members 124accommodated in the pipe member 122. The pipe member 122 has a pluralityof holes 126 on the outer circumference. The water can be penetratedthrough the holes 126 into the pipe member 122. The surfaceconfiguration of the wire member 124 is irregular in the same manner asin the wire member 90.

FIG. 11 shows a partial perspective view illustrating a porouswater-absorbing tube 130 which constitutes a fuel cell stack accordingto a third embodiment of the present invention, and FIG. 12 shows apartial perspective view illustrating a porous water-absorbing tube 140which constitutes a fuel cell stack according to a fourth embodiment ofthe present invention.

The porous water-absorbing tube 130 has a large number of holes 132,comprising an angular pipe member 134 having a square cross section, anda plurality of wire members 136 arranged in the angular pipe member 134.The porous water-absorbing tube 140 has a large number of holes 142,comprising a triangular pipe member 144 having a triangular crosssection, and a plurality of wire members 146 arranged in the triangularpipe member 144. The angular pipe member 134 and the triangular pipemember 144 are arranged along the shape of the corners of the outletside oxygen-containing gas communication hole 38 b and the outlet sidefuel gas communication hole 36 b.

In the porous water-absorbing tubes 120, 130, 140 constructed asdescribed above, the water permeates through the respective holes 126,132, 142. The same effect as that obtained in the first embodiment isobtained. That is, for example, it is possible to discharge the watersmoothly and reliably owing to the capillary phenomenon of the pluralityof wire members 124, 136, 146 and the difference in pressure of air.

FIG. 13 shows a longitudinal sectional view illustrating a fuel cellstack 160 according to a fifth embodiment of the present invention. Inthe fuel cell stack 160, porous water-absorbing tubes 162 are arrangedfor the outlet side oxygen-containing gas communication hole 38 b andthe outlet side fuel gas communication hole 36 b. The porouswater-absorbing tube 162 comprises a pipe member 164 and a plurality ofwire members 166 arranged at the inside of the pipe member 164.

The pipe member 164 is provided with a plurality of holes 168 which areformed at portions to be arranged at the outlet side oxygen-containinggas communication hole 38 b and the outlet side fuel gas communicationhole 36 b, making it possible to effect the permeation of water. On theother hand, no hole is provided at the portion exposed to the outside ofthe fuel cell stack 160. The pipe member 164 is constructed in anintegrated manner. However, it is also preferable that a tube providedwith the holes 168 and a tube having no hole are separately provided,and they are fixed by means of a joint or the like. It is alsopreferable to use a variety of water-absorbing members in place of thewire member 166.

FIG. 14 shows a vertical sectional view illustrating a porouswater-absorbing tube 180 which constitutes a fuel cell stack accordingto a sixth embodiment of the present invention. The porouswater-absorbing tube 180 comprises a water-absorbing member 182 having asolid cross section which is embedded on the lower side in the directionof the gravity of each of the outlet side oxygen-containing gascommunication hole 38 b and the outlet side fuel gas communication hole36 b. The water-absorbing member 182 is composed of, for example,sponge. The upper surface of the water-absorbing member 182 is set atthe position to provide a predetermined gap S from the secondoxygen-containing gas connecting flow passage 48 and the second fuel gasconnecting flow passage 66. It is possible to avoid any back flow ofwater.

FIG. 15 shows a schematic longitudinal sectional view illustrating afuel cell stack 200 according to a seventh embodiment of the presentinvention.

The fuel cell stack 200 comprises a bypass plate 202 which is tightenedand fastened by the tie rods 84 together with the second end plate 82.As shown in FIGS. 16, 17, and 18, the bypass plate 202 is arranged intight contact with the surface 14 b of the first separator 14 which isdisposed on the deep side of the inlet side oxygen-containing gascommunication hole 38 a and the outlet side oxygen-containing gascommunication hole 38 b of the fuel cell stack 200, i.e., on the deepside as viewed from a supply port K of the inlet side oxygen-containinggas communication hole 38 a and a discharge port H of the outlet sideoxygen-containing gas communication hole 38 b as shown in FIG. 19 asdescribed later on. An inlet side oxygen-containing gas communicationhole 38 a of the bypass plate 202 is provided at the positioncorresponding to the inlet side oxygen-containing gas communication hole38 a of the first separator 14.

Discharge holes 204 for supplying the oxygen-containing gas to be usedfor the reaction, which are provided for the bypass plate 202, aredisposed at positions corresponding to a bottom T2 of the outlet sideoxygen-containing gas communication hole 38 b of the first separator 14in a direction directed along the outlet side oxygen-containing gascommunication hole 38 b of the first separator 14.

As shown in FIGS. 16 and 17, bypass flow passages 208, which makecommunication between the outlet holes 204 and a plurality of inletholes 206 having rectangular cross sections formed at the hole wall ofthe inlet side oxygen-containing gas communication hole 38 a of thebypass plate 202, are provided on the surface 202 b of the bypass plate202 on the side opposite to the surface 202 a to make tight contact withthe first separator 14.

The bypass flow passages 208 includes three groove-shaped supplypassages 208 a which makes connection over a range from the inlet sideoxygen-containing gas communication hole 38 a to the discharge holes 204at diagonal positions, and two auxiliary supply passages 208 b whichextend from the inlet holes 206 along the upper and lower supplypassages 208 a of the supply passages 208 a and which are merged intothe supply passages 208 a at intermediate positions.

As shown in FIG. 17, as for the inlet side oxygen-containing gascommunication hole 38 a of the bypass plate 202, the bottom T1, whichprovides an opening position of the lowermost inlet hole 206, is set ata position (also shown in FIG. 18) that is lower by a height Δh1 thanthe inlet side oxygen-containing gas communication hole 38 a of thefirst separator 14. The discharge hole 204 is located at the bottom T2of the outlet side oxygen-containing gas communication hole 38 b of thefirst separator 14. The discharge hole 204 is opened at a position whichis lower by a height Δh2 than the position of the lowermost secondoxygen-containing gas connecting flow passage 48.

In order to avoid the back flow, the upper two of the supply passages208 a are bent at positions just before the discharge holes 204, andthey are formed and directed downwardly. The auxiliary supply passages208 b are also bent at positions just before the merging points P of thesupply passages 208 a, and they are formed and directed downwardly.

The bypass plate 202 constructed as described above is tightened andfastened by the tie rods 84 together with the end plate 82 as shown inFIG. 15 in a state in which a terminal plate 210 and an insulating plate212 are allowed to intervene as shown in FIG. 18. Therefore, strictlyspeaking, the bypass flow passages 208 are formed between the bypassplate 202 and the terminal plate 210.

The bypass flow passages 208 are designed so that the oxygen-containinggas flows in a flow rate which is not less than a flow rate of the flowof the oxygen-containing gas through the fuel cell unit 12.

As schematically shown in FIG. 19, in the fuel cell stack 200, the deepportion of the inlet side oxygen-containing gas communication hole 38 aand the deep portion of the outlet side oxygen-containing gascommunication hole 38 b are connected to one another by the bypass flowpassages 208 formed, for example, by the bypass plate 202 and the endplate 82. Accordingly, a return flow structure is formed, in which thesupply port K of the inlet side oxygen-containing gas communication hole38 a as the side to supply the oxygen-containing gas and the dischargeport H of the outlet side oxygen-containing gas communication hole 38 bas the side to discharge the gas after the reaction are provided on thesame side, i.e., on the first side surface side of the fuel cell stack200. In this arrangement, the single bypass plate 202, which has thethin plate-shaped configuration, is used. Therefore, the structure isadvantageous in that no piping is required at the outside of the fuelcell stack 200. It is possible to shorten the size of the fuel cell unit12 in the stacking direction.

The supply port K and the discharge port H are disposed on the sameside. Therefore, a merit is obtained such that the piping for the supplyport K and the discharge port H can be provided as collected pipingwhich is advantageous in the number of assembling steps and the numberof parts.

In the seventh embodiment constructed as described above, the productwater tends to stay on the deep side of the outlet sideoxygen-containing gas communication hole 38 b as compared with the frontside. However, a part of the oxygen-containing gas, which is supplied tothe inlet side oxygen-containing gas communication hole 38 a, passesfrom the inlet hole 206 of the bypass plate 202 through the bypass flowpassages 208 as shown in FIG. 19, and it is ejected at the dischargehole 204 to the outlet side oxygen-containing gas communication hole 38b. Accordingly, the product water, which is retained at the deep portionof the outlet side oxygen-containing gas communication hole 38 b, isextruded toward the discharge port H. This arrangement is also preferredespecially in the case of application to the vehicle which runs in aninclined state.

In this arrangement, as shown in FIG. 17, the auxiliary supply passages208 b are merged into the supply passages 208 a of the bypass flowpassages 208. Therefore, the flow rate is increased at the dischargehole 204. It is possible to efficiently extrude the product water at thedischarge hole 204. In this arrangement, the position of the dischargehole 204 (position of the bottom T2 of the outlet side oxygen-containinggas communication hole 38 b) is set to be lower by Δh2 than that of thesecond oxygen-containing gas connecting flow passage 48. Therefore,there is no fear of back flow.

On the other hand, the water is generated in some cases due to thecondensation of water vapor at the inlet side oxygen-containing gascommunication hole 38 a, because the oxygen-containing gas ishumidified. However, the position of the inlet hole 206 of the bypassflow passage 204 (position of the bottom T1 of the inlet sideoxygen-containing gas communication hole 38 a of the bypass plate 202)is set to be lower by Δh1 than that of the bottom of the inlet sideoxygen-containing gas communication hole 38 a, for example, of the firstseparator 14 and the first gasket 28. Therefore, it is also possible toefficiently discharge the condensed water.

Therefore, in the seventh embodiment, the drainage performance isremarkably improved for the retained product water and the condensedwater, and it is possible to avoid the deterioration of the powergeneration performance, by forcibly extruding the oxygen-containing gasfrom the discharge hole 204 by the aid of the bypass flow passage 202,in addition to the improvement in drainage performance owing to thecapillary phenomenon of the porous water-absorbing tube 86 and thedifference in pressure of air in the outlet side oxygen-containing gascommunication hole 38 b.

The bypass flow passage 202 used in the seventh embodiment describedabove may be incorporated into any one of the second to fifthembodiments.

FIG. 20 diagrammatically shows a fuel cell stack 220 according to aneighth embodiment of the present invention. Specifically, FIG. 20 showsanother embodiment of the bypass flow passage 202.

The eighth embodiment is different from the seventh embodiment as shownin FIG. 19. The supply port K of the inlet side oxygen-containing gascommunication hole 38 a and the discharge port H of the outlet sideoxygen-containing gas communication hole 38 b are provided on differentsides, i.e., on the sides of the opposing surfaces of the fuel cellstack 220.

In the eighth embodiment, the supply port K is arranged on the same sideas the deep side of the outlet side oxygen-containing gas communicationhole 38 b. Therefore, the oxygen-containing gas for the inlet sideoxygen-containing gas communication hole 38 a is branched with abranched tube 222, and it is supplied to the outlet sideoxygen-containing gas communication hole 38 b.

Accordingly, also in this case, the product water, which is retained atthe deep portion of the outlet side oxygen-containing gas communicationhole 38 b, can be extruded from the discharge port H. During thisprocess, when the condensed water is retained at the deep portion andthe front portion of the inlet side oxygen-containing gas communicationhole 38 a, the condensed water on the side of the inlet sideoxygen-containing gas communication hole 38 a can be also smoothlydischarged by providing a bypass passage 224 as shown by dashed lines inFIG. 20.

FIG. 21 diagrammatically shows a fuel cell stack 230 according to aninth embodiment of the present invention. Even in the case of thearrangement of the inlet side oxygen-containing gas communication hole38 a and the outlet side oxygen-containing gas communication hole 38 bin the same manner as in FIG. 20, a piping 232 can be detoured toconnect the deep portion of the inlet side oxygen-containing gascommunication hole 38 a and the front portion of the outlet sideoxygen-containing gas communication hole 38 b. Also in this case, in thesame manner as in the eighth embodiment described above, it is possibleto reliably discharge the product water at the deep portion of theoutlet side oxygen-containing gas communication hole 38 b and thecondensed water at the inlet side oxygen-containing gas communicationhole 38 a.

The present invention is not limited to the respective embodimentsdescribed above. For example, in place of the provision of the bypassplate 202 of the seventh embodiment, a bypass piping for connecting theinlet side oxygen-containing gas communication hole 38 a and the outletside oxygen-containing gas communication hole 38 b may be provided atthe outside of the second end plate 82. The respective embodiments areillustrative of the case in which the discharge hole 204 and the porouswater-absorbing tube are simultaneously used. However, the porouswater-absorbing tube may be abolished, and only the discharge hole 204may be provided, provided that the product water or the like issufficiently discharged. Alternatively, a plurality of discharge holes204 may be provided in the length direction of the outlet sideoxygen-containing gas communication hole 38 b to extrude the productwater from an intermediate portion as well as the deep portion as viewedfrom the side of the discharge port H of the outlet sideoxygen-containing gas communication hole 38 b.

FIG. 22 shows a schematic sectional view illustrating a fuel cell stack240 according to a tenth embodiment of the present invention.

Reference numeral 242 indicates a terminal plate, and reference numeral244 indicates an insulator plate. The terminal plate 242 and theinsulator plate 244 are overlapped with the second separator 16 in anorder of the terminal plate 242 and the insulator plate 244 on the sideof the first end plate 80, and they are tightened and fastened togetherwith the first end plate 80 by means of the tie rods 84. On the otherhand, the terminal plate 242 and the insulator plate 244 are overlappedwith the first separator 14 in an order of the terminal plate 242 andthe insulator plate 244 on the side of the second end plate 82, and theyare tightened and fastened together with the second end plate 82 bymeans of the tie rods 84.

Each of the terminal plate 242 and the insulator plate 244 on the sideof the first end plate 80 is also provided, at both end portions in thelateral direction, with an inlet side fuel gas communication hole 36 a,an inlet side oxygen-containing gas communication hole 38 a, an inletside cooling medium communication hole 40 a, an outlet side coolingmedium communication hole 40 b, an outlet side fuel gas communicationhole 36 b, and an outlet side oxygen-containing gas communication hole38 b. The first end plate 80 is formed with a hole 94 which communicateswith the outlet side oxygen-containing gas communication hole 38 b. Amanifold tube 98, which communicates with the hole 94, is connected tothe first end plate 80 by the aid of a joint 246.

The manifold tube 98 includes an outer tube (gas flow passage) 100 whichextends from the joint 246. The outer tube 100 rises upwardly, and it isopen to the atmospheric air. A back pressure valve 248 for adjusting thepressure in the fuel cell stack 240 is provided at an intermediateposition of the outer tube 100. A drainage pipe (suction member) 250 isinserted into the outlet side oxygen-containing gas communication hole38 b and the hole 94 of the first end plate 80 in a state of making nocontact with the surroundings.

As shown in FIGS. 23 to 25, the drainage pipe 250 is applied to a resincoating for the outer wall in order to ensure the insulation performancewith respect to the inner wall of the outlet side oxygen-containing gascommunication hole 38 b. A resin end cap 252 is attached to the end ofthe insertion side in order to ensure the insulation performance aswell. The drainage pipe 250 is supported in a state of being insertedinto a fitting hole 242 a which is formed for the terminal plate 242disposed on the side of the second end plate 82.

A suction hole (opening) 254, which is open in the outlet sideoxygen-containing gas communication hole 38 b, is provided at the lowerwall at the end on the insertion side of the drainage pipe 250, i.e., onthe lower side in the direction of the gravity. A stay plate 256 isattached to the outer circumference at the end on the first end plate 80of the drainage pipe 250. The stay plate 256 is positioned with respectto the first end plate 80, and it is tightened together with the joint246. Therefore, a merit is obtained such that the stay plate 256 can beused to correctly set the drainage pipe 250 in the outlet sideoxygen-containing gas communication hole 38 b. The end of the drainagepipe 250 on the side of the first end plate 80 slightly protrudes fromthe first end plate 80.

A bypass tube (outlet side flow passage) 258 is connected to thedrainage pipe 250 formed as described above. As shown in FIG. 22, thebypass tube 258 has one end which is connected to the drainage pipe 250,and the other end which is connected to the downstream side of the backpressure valve 248. As shown in FIG. 23, a female connector 258 a isattached to the one end of the bypass tube 258. The drainage pipe 250 isfitted and connected to the female connector 258 a. The female connector258 a is inserted and fixed into the joint 246 in a state of penetratingthrough the joint 246. A seal ring S for sealing the drainage pipe 250is provided on the inner circumferential surface of the female connector258 a.

A ring member 260, which is provided with a seal ring S on the outercircumferential surface, is attached in the vicinity of the attachmentportion of the bypass tube 258 to the female connector 258 a. The ringmember 260 is inserted in a sealed state into the inner circumferentialsurface of a pipe support holder 262 which is provided around theinsertion section of the outer tube 100. The joint 246 of the manifoldtube 98 constructed as described above is tightened and fastened to thefirst end plate 80 together with the stay plate 256 by the aid of boltsB.

A hole 104, which communicates with the outlet side fuel gascommunication hole 36 b, is formed for the first end plate 80. Amanifold tube 106, which is constructed in the same manner as themanifold tube 98 described above, is connected to the hole 104. Thedrainage pipe 250 is inserted into the hole 104. The bypass tube 258 isconnected in communication with the drainage pipe 250. These structuresand the like are the same as those of the outlet side oxygen-containinggas communication hole 38 b. The same components are designated by thesame reference numerals, detailed explanation of which will be omitted.

As shown by chain lines in FIG. 22, a throttle section 264 is providedat the inside of the outer tube 100 at the connecting portion of thebypass tube 258 connected to the downstream side of the back pressurevalve 248. Accordingly, an ejector section 266 can be formed by thebypass tube 258 and the throttle section 264 as well.

The operation of the fuel cell stack 240 according to the tenthembodiment constructed as described above will be explained below.

During the operation of the fuel cell stack 240, the pressure in thesystem is adjusted to be constant by the aid of the back pressure valve248. Therefore, a certain differential pressure is generated between theupstream side and the downstream side of the back pressure valve 248.The difference in pressure is generated by the differential pressurebetween the side of the first end plate 80 and the side of the backpressure valve 248 of the bypass tube 258. As a result, the productwater in the outlet side oxygen-containing gas communication hole 38 bis sucked from the suction hole 254 of the drainage pipe 250. Theproduct water passes through the bypass tube 258, and it is dischargedtogether with the reacted gas from the manifold tube 98 to the outsideof the system.

Similarly, for example, the product water, which is generated bycondensation of the water vapor of the fuel gas stored in the outletside fuel gas communication hole 36 b, is also sucked from the suctionhole 254 of the drainage pipe 250. The product water passes through thebypass tube 258, and it is discharged together with the reacted gas fromthe manifold tube 98 to the outside of the system.

Accordingly, when the product water or the like is retained in theoutlet side oxygen-containing gas communication hole 38 b and the outletside fuel gas communication hole 36 b, then the product water can besucked from the suction hole 254 of the drainage pipe 250, and it can bedischarged to the outside. Therefore, it is possible to improve thedrainage performance for the product water or the like retained in theoutlet side oxygen-containing gas communication hole 38 b and the outletside fuel gas communication hole 36 b, and it is possible to avoid thedeterioration of the power generation performance, which would beotherwise caused by the back flow of water droplets into thepower-generating surface. That is, the water is discharged by thesuction based on the differential pressure not by the gravity.Therefore, it is possible to perform the drainage quickly and reliably.

As a result, even when the water is retained on the deep side of theoutlet side oxygen-containing gas communication hole 38 b and the outletside fuel gas communication hole 36 b disposed on the side opposite tothe first end plate 80, the water can be reliably discharged. Therefore,this arrangement is preferred when the fuel cell stack 240 is used forthe vehicle in which the fuel cell stack 240 is used in an inclinedstate.

Further, the product water, which tends to be retained on the lower sideby the gravity, can be sucked and removed by using the drainage pipe 250from the outlet side oxygen-containing gas communication hole 38 b andthe outlet side fuel gas communication hole 36 b disposed on the lowerside in the direction of the gravity. Therefore, it is possible toefficiently discharge the water from the lower portions in the directionof the gravity in which the back flow to the power-generating surface isapt to occur, and a large amount of product water or the like isretained. In this arrangement, it is possible to reliably discharge thewater from the outlet side oxygen-containing gas communication hole 38 band the outlet side fuel gas communication hole 36 b by the aid of thesuction hole 254 formed on the lower side in the direction of thegravity.

Further, the back pressure valve 248, which is provided for the outletside oxygen-containing gas communication hole 38 b and the outlet sidefuel gas communication hole 36 b, is effectively utilized to make itpossible to suck and remove the product water retained in the outletside oxygen-containing gas communication hole 38 b and the outlet sidefuel gas communication hole 36 b from the suction hole 254 of thedrainage pipe 250. Therefore, it is unnecessary to provide anyadditional pump or the like, and is possible to simplify the structure.As described above, when the ejector section 264 is provided, it ispossible to perform the drainage more effectively, because the force fordrawing the water by the drainage pipe 250 is increased by the ejectoraction.

In the fuel cell stack 240 described above, the piping is attached toonly one side of the end plate. Therefore, the following effect isobtained. That is, it is possible to decrease the piping space, it ispossible to use the collective piping, and thus the piping structure issimplified.

In the tenth embodiment described above, for example, the drainage pipe250 described above may be also provided for the inlet side fuel gascommunication hole 36 a and the inlet side oxygen-containing gascommunication hole 38 a. In this arrangement, it is possible to avoidany invasion of water droplets into the power-generating surface fromthe inlet side fuel gas communication hole 36 a and the inlet sideoxygen-containing gas communication hole 38 a.

The tenth embodiment is illustrative of the case in which the drainagepipe 250 is provided for the outlet side oxygen-containing gascommunication hole 38 b and the outlet side fuel gas communication hole36 b. However, for example, it is also preferable that the drainage pipe250 is provided for only the side of the outlet side oxygen-containinggas communication hole 38 b in which a large amount of product water isretained. The position of the suction hole 254 formed for the drainagepipe 250 is not limited to the end portion on the side of the second endplate 82. The suction hole 254 may be provided at the end portion on theside of the first end plate 80. In this arrangement, even when the fuelcell stack 240 is inclined toward either the first end plate 80 or thesecond end plate 82, it is possible to discharge the water from eithersuction hole 254 in a reliable manner. Of course, a plurality of suctionholes may be provided over an entire region of the insertion section ofthe drainage pipe 250.

The formation portion is not limited to the outer circumferential edgeportion provided that the inlet side fuel gas communication hole 36 a,the inlet side oxygen-containing gas communication hole 38 a, the outletside fuel gas communication hole 36 b, and the outlet sideoxygen-containing gas communication hole 38 b are formed in the planesof the first and second separators 14, 16.

In the fuel cell stack according to the present invention, thecommunication holes for allowing the reaction gas to flow are providedat the outer circumferential edge portions on the side of the separator.Accordingly, it is possible to shorten the size in the height directionas small as possible, and it is easy to realize the thin type. Further,the water in the communication hole can be discharged smoothly andreliably owing to the capillary phenomenon and the difference inpressure of the reaction gas by the aid of the porous water-absorbingtube arranged in the communication hole. Accordingly, even when the fuelcell stack is arranged in an inclined manner due to any inclination ofthe vehicle or the like, then the back flow of the water to the gas flowpassage can be effectively excluded, the power generation performancecan be ensured, and it is possible to greatly improve the drainageperformance with the simple structure.

According to the present invention, even if the product water or thelike is retained in the outlet side communication hole, when thereaction gas is supplied from the discharge hole, then the product wateror the like, which is retained in the outlet side communication hole, isextruded by the reaction gas ejected from the discharge hole. Therefore,it is possible to improve the drainage performance for the product wateror the like retained in the outlet side communication hole, especiallythe drainage performance for the product water or the like which isretained at the deep portion and which is difficult to be discharged.Accordingly, it is possible to enhance the drainage performance for theproduct water or the like even when the size of the entire fuel cellstack in the stacking direction is long.

Further, according to the present invention, when the product water orthe like is retained in the inlet side communication hole or the outletside communication hole, then the product water can be sucked from theopening of the suction member, and it can be discharged to the outside.Therefore, it is possible to improve the drainage performance for theproduct water or the like retained in the inlet side communication holeor the outlet side communication hole. As for the inlet sidecommunication hole, it is possible to avoid any invasion of waterdroplets into the power-generating surface. As for the outlet sidecommunication hole, it is possible to avoid any back flow of waterdroplets into the power-generating surface. Thus, it is possible toavoid the deterioration of the power generation performance.

1. A fuel cell stack formed by stacking a plurality of fuel cell unitseach including an anode electrode, a cathode electrode, and a solidpolymer ion exchange membrane interposed between said anode electrodeand said cathode electrode, and separators sandwiching said fuel cellunit, said fuel cell units and said separators being stacked in ahorizontal direction, said fuel cell stack including: a supply holeextending through said separators, for supplying a reaction gas to saidfuel cell units; a discharge hole extending through said separators, fordischarging said reaction gas from said fuel cell units after saidreaction gas is used in reaction in said fuel cell units; a drainagepipe disposed within said discharge hole and extending at least partlythrough said separators; and at least first and second pipes providedoutside said fuel cell units, said first and second pipes being directlyconnected to said discharge hole wherein a valve is disposed in saidfirst pipe, and wherein one end of the second pipe is coupled to saiddrainage pipe, and an opposite end of said second pipe is coupled tosaid first pipe at a position downstream of said valve.
 2. The fuel cellstack according to claim 1, wherein said first pipe is a reaction gasdischarge pipe for discharging said reaction gas from said fuel cellunits; and said second pipe is a water discharge pipe for dischargingwater produced in reaction in said fuel cell units.
 3. The fuel cellstack according to claim 2, wherein said reaction gas discharge pipe isslanted upwardly from said discharge hole.
 4. The fuel cell stackaccording to claim 2, wherein said water discharge pipe is connected tosaid drainage pipe provided in said discharge hole, and said drainagepipe has an opening for allowing passage of water produced in said fuelcell units into the drainage pipe.
 5. The fuel cell stack according toclaim 4, wherein an outlet of said water discharge pipe is connected tosaid reaction gas discharge pipe at a position downstream of a backpressure valve connected to said reaction gas discharge pipe.
 6. Thefuel cell according to claim 4, wherein said reaction gas discharge pipeincludes an ejector having a throttle section, and said ejector isconnected to said water discharge pipe.
 7. The fuel cell stack accordingto claim 4, wherein said opening of said drainage pipe is provided at alower end thereof and oriented downwardly.
 8. The fuel cell stackaccording to claim 1, further comprising a connector element disposedbetween the drainage pipe and the second pipe for coupling said drainagepipe to said second pipe.
 9. The fuel cell according to claim 8, whereinsaid connector element comprises a first end having an opening sized anddimensioned for receiving one end of said second pipe and a secondopposed end having an opening sized and dimensioned for receiving oneend of said drainage pipe.
 10. The fuel cell stack according to claim 9,wherein said connector element further comprises a seal member providedon an inner surface of said connector element, wherein said seal membercontacts an outer surface of said drainage pipe when disposed withinsaid opening of said second end.